FIG. 1 schematically illustrates a communications device. The device 10 of FIG. 1 is a transceiver (i.e., a transmitter and a receiver) which forms part of a cellular phone, cordless phone or personal digital assistant (PDA). The device 10 of FIG. 1 may be viewed as comprising a baseband subsystem 12 and an RF (radio frequency) subsystem 14.
In the transmitting mode, the baseband subsystem 12 receives data from a source and codes the data in a sequence of in-phase (I) and a sequence of quadrature (Q) channel symbols. The I and Q channel symbols are then fed to the RF subsystem 14 which modulates these symbols onto one or more RF carrier signals for remote transmission.
In the receiving mode, the RF subsystem 14, receives one or more RF carrier signals and demodulates from the received RF carrier signals a sequence of I and Q symbols. The I and Q symbols are delivered to the baseband subsystem 12 which decodes these I and Q symbols to regenerate source data.
For a variety of reasons it may be desirable to provide the capability for testing the RF subsystem of a communications device without the baseband subsystem. For example, during the design of a mobile communication device, the baseband and RF subsystems may be designed separately. Under such circumstances, it may be desirable to test the RF subsystem before the baseband subsystem is available. Alternatively, even if the baseband subsystem is available, it may be desirable to test the RF subsystem separately so that faults in the RF subsystem can be more easily located and identified.
Accordingly, it is an object of the present invention to provide a system which simulates a baseband subsystem in a communications transceiver.